The various wheels and rollers that guide the track of a tracklaying vehicle and that support the vehicle on the track are typically provided with bumpers so that the vehicle, which may be a crane, earthmover, steam shovel, or the like, can move along highly irregular ground without damaging these parts of its track suspension. In particular when a rock or the like comes between the track and one of its wheels or rollers it is necessary that this wheel or roller be able to deflect inwardly considerably. At the same time this deflection must be resisted with a considerable force. (See pp. 385-9. Principles of Automotive Vehicles, U.S. Gov't Printing Office, Washington, D.C. 1956).
The typical such element is simply formed as a preloaded or prestressed unit having a bumper plate and a mounting plate one of which is welded to one end of a rod whose other end passes through a hole in the other plate and has a head to the other side of this other plate. Thus the two plates can move toward each other. A very heavy compression spring is braced in compressed condition between these two plates so that when the bumper plate engages the support arm or the like of the respective wheel or roller it resists further displacement of this support arm with a considerable force.
Such an arrangement has two considerable disadvantages. First of all it is a relatively difficult matter to assemble and service this welded-together unit. Checking the condition of the welds is almost impossible and any adjustment of the prestressing of the spring is also impossible. Furthermore such units break occasionally and present an enormous hazard to any nearby person, as once the rod or stem between the two plates breaks or becomes disattached from either plate a bumper plate is thrown out violently by the spring. Indeed it is possible for such a bumper plate to be ejected with such force that it can cause grave injury or death to a nearby person. It is not uncommon for the compression spring to be prestressed with a force in the neighborhood of 20Mp. (20,000 Kg force).